The present invention relates generally to scheduling of user terminals on an uplink shared channel in a mobile communication system and, more particularly, to a method of multi-frame allocation to enable the aggregation of symbol energies over multiple frames for greater efficiency.
The WiMax standard supports both time division duplex (TDD) and frequency division duplex (FDD) operation. In the case of TDD, the uplink and downlink transmissions occur at different times and usually share the same frequency. Time is divided into a sequence of consecutive frames. Each frame has a fixed duration and contains one downlink sub-frame and one uplink sub-frame. The frame is divided into an integer number of OFDM symbols. The number of symbols allocated to the downlink sub-frame and uplink sub-frame is variable.
The medium access control (MAC) protocol for WiMax currently requires that a single MAC protocol data unit (PDU) must be transmitted in one frame. This requirement may result in some inefficiencies. Because user terminals are power limited, it is generally desirable to reduce the number of sub-channels allocated to a single user terminal when the user terminal is operating near the cell edge. Reducing the number of sub-channels enables the user terminal to allocate more power to each sub-channel, thereby increasing the information bit signal-to-noise ratio. The increase in the information bit signal-to-noise ratio due to reduction of sub-channels (greater sub-channelization) is referred to as sub-channelization gain. However, the reduction in the number of sub-channels limits the available bandwidth for the user terminal. The bandwidth limitation may prevent the user terminal from using the most robust modulation and coding scheme. Further, the bandwidth limitation may increase overhead on both the uplink and downlink. When the size of an uplink burst is limited because of sub-channelization, the size of the MAC PDU payload is reduced and the overhead ratio, i.e., the ratio of overhead bits to total bits, is increased. Thus, the effective data rate on the uplink is reduced.